1. Field of the Invention
The present invention relates to a porous region removing method and a semiconductor substrate manufacturing method and, more particularly, to a method of removing a porous region from a substrate having the porous region, a semiconductor substrate manufacturing method using this method, and an apparatus for removing a porous region.
2. Description of the Related Art
There is a method of sequentially forming a porous Si layer and a single-crystal Si layer on a first substrate, bonding the first substrate to a separately prepared second substrate, and separating the bonded substrate stack into two substrates at the porous Si layer to transfer the single-crystal Si layer formed on the first substrate side to the second substrate side, thereby manufacturing an SOI substrate.
In this method, after the bonded substrate stack is separated into two substrates, the porous Si layer remaining on the surface on the second substrate side is removed. In removing the porous Si layer, the planarity of the surface of the underlying second substrate and, more particularly, the film thickness uniformity of the single-crystal Si layer as the surface layer of the second substrate is preferably not hindered.
The present invention has been made in consideration of the above situation, and has as its object to provide a porous region removing method capable of maintaining a given planarity of an underlying layer and a semiconductor substrate manufacturing method using this method.
According to the present invention, there is provided a porous region removing method for removing a porous region from a substrate having the porous region, characterized by comprising the first step of filling the porous region with a first process solution having no etching function or weak etching function for a porous material, and the second step of etching the porous region using a second process solution having an etching function for a porous material after the first step.
In the porous region removing method, the second step preferably comprises replacing the first process solution filling the porous region with the second process solution to etch the porous region.
In the porous region removing method, the substrate to be processed preferably essentially consists of single-crystal Si.
In the porous region removing method, the porous region preferably essentially consists of an Si material.
In the porous region removing method, the porous region is preferably formed by anodizing a substrate consisting of single-crystal Si.
In the porous region removing method, preferably, the first process solution chemically changes pore walls in the porous region, and the second process solution has the etching function not only for a porous material but also for a substance which chemically changes.
In the porous region removing method, the first process solution preferably has an oxidation function for the pore walls in the porous region.
In the porous region removing method, the first process solution is preferably water.
In the porous region removing method, the first process solution preferably contains a material selected from the group consisting of an alcohol, hydrogen peroxide, nitric acid, and hydrochloric acid.
In the porous region removing method, the second process solution preferably contains hydrofluoric acid.
In the porous region removing method, the second process solution is preferably a material selected from the group consisting of
(a) a mixed solution prepared by adding at least one of an alcohol and hydrogen peroxide to hydrofluoric acid,
(b) a mixed solution of hydrofluoric acid and nitric acid, and
(c) a mixed solution of hydrofluoric acid, nitric acid, and acetic acid.
In the porous region removing method, an ultrasonic wave is preferably supplied to the substrate during at least part of an overall period of execution of the first and second steps.
In the porous region removing method, the first step preferably comprises supplying an ultrasonic wave to the substrate.
In the porous region removing method, an ultrasonic wave is preferably supplied to the substrate during at least part of an overall period of execution of the second step.
In the porous region removing method, an ultrasonic wave is preferably supplied to the substrate during at least part of an overall period of execution of the second step, in which the first process solution filling the porous region is replaced with the second process solution.
In the porous region removing method, the second step preferably comprises the steps of etching the porous region without supplying any ultrasonic wave to the substrate until the pore walls in the porous region have not more than a predetermined thickness, and etching the porous region remaining on the substrate while supplying an ultrasonic wave to the substrate, thereby removing the porous region.
In the porous region removing method, the second step preferably comprises the steps of replacing the first process solution filling the porous region with the second process solution while supplying an ultrasonic wave to the substrate, etching the porous region without supplying any ultrasonic wave to the substrate until the pore walls in the porous region have not more than a predetermined thickness, and etching the porous region remaining on the substrate while supplying an ultrasonic wave to the substrate, thereby removing the porous region.
The porous region removing method preferably further comprises, after the second step, the third step of removing the porous region remaining on the substrate.
In the porous region removing method, the third step preferably comprises removing the porous region remaining on the substrate using an etchant.
In the porous region removing method, the third step preferably comprises removing the porous region remaining on the substrate using the etchant while supplying the ultrasonic wave to the substrate.
In the porous region removing method, the second and third steps are preferably executed while dipping the substrate to be processed in the same etchant.
In the porous region removing method, the third step preferably comprises removing the porous region remaining on the substrate using a third process solution whose etching rate for the porous material is higher than that of the second process solution.
In the porous region removing method, the third step preferably comprises removing the porous region remaining on the substrate using a high-pressure fluid.
In the porous region removing method, the third step preferably comprises removing the porous region remaining on the substrate by polishing.
In the porous region removing method, the third step preferably comprises removing the porous region remaining on the substrate by scrubbing.
In the porous region removing method, in processing the substrate while supplying the ultrasonic wave to the substrate, a relative positional relationship between the substrate and an ultrasonic source is preferably changed.
In the porous region removing method, in processing the substrate while supplying the ultrasonic wave to the substrate, the substrate is preferably swung in the process solution.
In the porous region removing method, in processing the substrate while supplying the ultrasonic wave to the substrate, a position of at least one of the substrate and the ultrasonic source is preferably changed in a direction substantially parallel or perpendicular to a vibration plane of the ultrasonic wave.
In the porous region removing method, the first and/or second step preferably comprises changing a relative positional relationship between the substrate and the ultrasonic source.
In the porous region removing method, all or some of the first to third steps preferably comprise changing a relative positional relationship between the substrate and the ultrasonic source.
In the porous region removing method, the first and/or second steps preferably comprises circulating the process solution to form a flow of the process solution near the substrate.
In the porous region removing method, all or some of the first to third steps preferably comprise circulating the process solution to form a flow of the process solution near the substrate.
In the porous region removing method, supply of the ultrasonic wave to the substrate is preferably controlled by operating or stopping the ultrasonic source.
In the porous region removing method, supply of the ultrasonic wave to the substrate is preferably controlled by inserting an ultrasonic wave shielding plate between the ultrasonic source and the substrate.
According to the present invention, there is also provided a method of manufacturing a semiconductor substrate, characterized by comprising the steps of forming a porous layer and at least one non-porous layer on a first substrate, bonding a second substrate to the non-porous layer side of the first substrate, removing the first substrate from the bonded substrate stack to expose the porous layer on a surface of the second substrate, and removing the porous layer on the second substrate using the above porous region removing method.
In the semiconductor substrate manufacturing method, the step of exposing the porous layer preferably comprises grinding, polishing, or etching the first substrate from a lower surface side of the bonded first substrate to expose the porous layer on the surface of the second substrate.
In the semiconductor substrate manufacturing method, the step of exposing the porous layer preferably comprises dividing the bonded substrate stack at the porous layer to expose the porous layer on the surface of the second substrate.
In the semiconductor substrate manufacturing method, the non-porous layer preferably includes a single-crystal Si layer.
In the semiconductor substrate manufacturing method, the non-porous layer preferably includes a single-crystal Si layer and an Si oxide layer.
In the semiconductor substrate manufacturing method, the single-crystal Si layer is preferably a layer epitaxially grown on the porous layer of the first substrate.
In the semiconductor substrate manufacturing method, the non-porous layer preferably includes a single-crystal compound semiconductor layer.
In the semiconductor substrate manufacturing method, the second substrate preferably essentially consists of an Si material.
In the semiconductor substrate manufacturing method, the second substrate preferably has an Si oxide layer on a surface to be bonded to the first substrate.
In the semiconductor substrate manufacturing method, the second substrate is preferably a transparent substrate.
According to the present invention, there is also provided a porous region removing apparatus for removing a porous region from a substrate having the porous region, characterized by comprising means for executing the first step of filling the porous region with a first process solution having no etching function or weak etching function for a porous material, and means for executing the second step of replacing the first process solution filling the porous region with the second process solution having an etching function for a porous material to etch the porous region.
Further objects, features and advantages of the present invention will become apparent from the following detailed description of embodiments of the present invention with reference to the accompanying drawings.